The present invention relates generally to a technique including a process and resulting structure for a copolymer resin for an ultra-shortwave light source such as KrF or ArF. More specifically, it relates to a copolymer resin, where a norbornyl(meth)acrylate unit is introduced to a copolymeric structure for a photo resist. The photo resist can be used in a variety of lithography processes using a KrF (248 nm) or ArF (193) light source which is a light source to be applied in next generation memory elements such as 1 G or 4 G DRAM integrated circuit chips.
In general, characteristics such as etching resistance, adhesiveness with low light absorption at 193 nm wavelength are often desired for a copolymer resin for ArF. The copolymer resin should also be developable by using, for example, a 2.38 wt % aqueous solution of tetramethylammonium hydroxide (TMAH). It is difficult, however, to synthesize a copolymer resin satisfying some or all these desirable characteristics. Many researches have often focused on studies on a norbolac type resin as a material to increase transparency at 193 nm wavelength and increase etching resistance. Thus, attempts to employ(meth)acrylate resins having high transparency, and to introduce alicyclic compounds to resin side chains in order to overcome limitations of deficient etching resistance, have been suggested. For example, IBM suggested the use of a copolymer resin represented by following chemical formula I: 
where R1, R2 and R3 independently represent hydrogen or methyl.
The copolymer resin represented by chemical formula I unfortunately has increased hydrophobicity. The increased hydrophobicity occurs, in part, from introducing an alicyclic compound to the side chain, which decreases solubility in the developing solution and weakens adhesiveness, so that the compound can be contained in the copolymer resin composition in an amount not more than a certain level. It should be noted that if the alicyclic compound is included at less than the certain level, satisfactory etching resistance cannot generally be achieved. It has been found that, among the conventional alicyclic groups on side chains, which are commonly known, the norbornyl or admantyl group is effective in view of etching resistance. The conventional copolymer resin including formula I has a severe limitation in that adhesive strength decreases by gaining hydrophobicity as the content of the cyclic compound in the resin composition increases.
From the above, it is seen that an improved photo resist that has improved characteristics is highly desirable.
The present inventors have performed intensive studies to overcome the above problems encountered in conventional photo resist products, and as a result, they found a copolymer resin composition having high transparency at 193 nm wavelength and high etching resistance.
In a specific embodiment, the present copolymer resin is prepared by radical polymerization techniques. These techniques include a variety of steps such as introducing norbornyl(meth)acrylate unit in a copolymer resin for photo resist. An adhesive strength of the resin can be increased by introducing a hydrophilic group in norbornyl group. A significant difference of solubility to the developing solution between the exposed region and non-exposed region can be provided through the processes of introducing a suitable protecting group, exposing, and deprotecting by post-heating step.
In an alternative embodiment, the present invention provides a monomer comprising a 5-hydroxy-6-norbornyl(meth)acrylate derivative. In a further embodiment, the present invention provides a process for preparing the monomer. In still a further embodiment, the present invention provides a copolymer resin comprising 5-hydroxy-6-norbornyl(meth)acrylate derivative and a process for preparing the copolymer resin. Among other aspects, the invention also provides photo resist comprising the copolymer resin or resins. Still further, the present invention provides a process for manufacturing the photo resist and a semiconductor element having a pattern formed by using the photo resist. These and other embodiments will be described throughout the present specification and more particularly below.
The present invention achieves these benefits in the context of known process technology. However, a further understanding of the nature and advantages of the present invention may be realized by reference to the latter portions of the specification and attached drawings.
In a specific embodiment, the present invention relates generally to a copolymer resin comprising 5-hydroxy-6-norbornyl(meth)acrylate derivative represented by chemical formula II: 
where R represents 2-tert-butoxycarbonyl, 2-carboxylic, 2-hydropyranyloxycarbonyl, 2-hydroxyfuranyloxycarbonyl or 2-ethoxyethyloxycarbonyl; R1 represents hydrogen or methyl.
The copolymer resin according to the present invention preferably includes copolymers represented by chemical formula III to VII.
(1) Poly[2-tert-butoxycarbonyl-5-hydroxy-6-norbornyl(meth)acrylate/2-carboxylic-5-hydroxy-6-norbornyl(meth)acrylate] copolymer resin (Molecular Weight: 4,000 to 100,000) 
[In the formula, R1 and R2 independently represent hydrogen or methyl, and x and y independently represent a mole fraction between 0.001 and 0.99.]
(2) Poly[2-tert-butoxycarbonyl-5-hydroxy-6-norbornyl(meth)acrylate/2-hydroxyethyl(meth)acrylic acid/(meth)acrylic acid] copolymer resin (Molecular Weight: 4,000 to 100,000) 
[In the formula, R1, R2 and R3 independently represent hydrogen or methyl,and x, y and z independently represent a molar fraction between 0.001 and 0.99.]
(3) Poly[2-hydroxypyranyloxycarbonyl-5-hydroxy-6-norbornyl(meth)acrylate/2-hydroxyethyl(meth)acrylate/(meth)acrylic acid] copolymer resin (Molecular Weight: 4,000 to 100,000) 
[In the formula, R1, R2 and R3 independently represent hydrogen or methyl, and x, y and z independently represent a mole fraction between 0.001 and 0.99.]
(4) Poly[2-hydrofuranyloxycarbonyl-5-hydroxy-6-norbornyl(meth)acrylate/2-hydroxyethyl(meth)acrylate/(meth)acrylic acid] copolymer resin (Molecular Weight: 4,000 to 100,000) 
[In the formula, R1, R2 and R3 independently represent hydrogen or methyl, and x, y and z independently represent a mole fraction between 0.001 and 0.99.]
(5) Poly[2-ethoxyethyloxycarbonyl-5-hydroxy-6-norbornyl(meth)acrylate/2-hydroxyethyl(meth)acrylate/(meth)acrylic acid] copolymer resin (Molecular Weight: 4,000 to 100,000) 
[In the formula, R1, R2 and R3 independently represent hydrogen or methyl, and x, y and z independently represent a mole fraction between 0.001 and 0.99.]
The copolymer resin of formula III according to the present invention can be prepared by reacting 2-tert-butoxycarbonyl-5-hydroxy6norbornyl(meth)acrylate with 2-carboxylic-5-hydroxy-6-norbornyl(meth)acrylate in the presence of a conventional polymerization initiator, as illustrated in reaction scheme I: 
where R1 and R2 independently represent hydrogen or methyl.
The copolymer resin of formula IV according to the present invention can be prepared by reacting 2-tert-butoxycarbonyl-5-hydroxy-6-norbornyl(meth)acrylate with 2-hydroxyethyl(meth)acrylate in the presence of a conventional polymerization initiator, as illustrated in reaction scheme II: 
where R1, R2 and R3 independently represent hydrogen or methyl.
The copolymer resin of formula V according to the present invention can be prepared by reacting 2-hydroxypyranyloxycarbonyl-5-hydroxy-6-norbornyl(meth)acrylate, 2-hydroxyethyl(meth)acrylate and (meth)acrylic acid in the presence of a conventional polymerization initiator, as illustrated in reaction scheme III: 
wherein, R1, R2 and R3 independently represent hydrogen or methyl.
The copolymer resin of formula VI according to the present invention can be prepared by reacting 2-hydrofuranyloxycarbonyl-5-hydroxy-6-norbornyl(meth)acrylate, 2-hydroxyethyl(meth)acrylate and (meth)acrylic acid in the presence of a conventional polymerization initiator, as illustrated in reaction scheme IV: 
where R1, R2 and R3 independently represent hydrogen or methyl.
The copolymer resin of formula VII according to the present invention can be prepared by reacting 2-ethoxyethyloxycarbonyl-5-hydroxy-6-norbornyl(meth)acrylate, 2-hydroxyethyl(meth)acrylate and (meth)acrylic acid in the presence of a conventional polymerization initiator, as illustrated in reaction scheme V: 
wherein R1, R2 and R3 independently represent hydrogen or methyl.
The copolymer resins (formula III to VII) according to the present invention can be prepared by a conventional polymerization process such as bulk polymerization or solution polymerization. Polymerization initiators usable in the present invention include benzoyl peroxide, 2,2xe2x80x2-azobisisobutyronitrile (AIBN), acetyl peroxide, lauryl peroxide, tert-butyl peracetate, di-tert-butyl peroxide, or the like. As a reaction solvent, cyclohexanone, methyl ethyl ketone, benzene, toluene, dioxane and/or dimethylformamide may be used individually, or in a mixture.
In the process for preparing the copolymer resin according to the present invention, general polymerization condition including temperature and pressure of radical polymerization may be controlled dependent upon the property of the reactants, but it is preferable to carry out the polymerization reaction at a temperature between 60 and 200 EC under nitrogen or argon atmosphere for 4 to 24 hours.
The copolymer resin according to the present invention can be used as a chemical amplification photoresist, which is prepared by polymerizing (meth)acrylate derivatives in which norbornyl group having a hydrophilic group has been introduced to the side chain. The photoresist has high glass transition temperature which is required in the course of the manufacturing process, and has rare absorption at 193 Fm, and the protective group therein can be easily removed. In addition, the norbornyl group synthesized to have hydrophilicity increases adhesiveness. The copolymer resin prepared according to the present invention can be advantageously used in lithography process, which is expected to be applied in 1 G or 4 G DRAM.
The copolymer resin of the present invention can be prepared according to a conventional process of photoresist composition, that is, by mixing conventional inorganic acid generator in the presence of organic solvent to manufacture photoresist solution. The photoresist can be used in the formation of positive micro-image. In the process for forming photoresist pattern of semiconductor element, the amount of the copolymer resin according to the present invention depends on the organic solvent or inorganic acid generator used, and the condition of lithography, but conventionally it is about 10 to 30% by weight on the basis of the organic solvent used in the preparation of the photoresist.
The process for forming a photoresist pattern of a semiconductor element by using the copolymer resin according to the present invention is described in detail here-in-below:
The copolymer resin according to the present invention is dissolved in cyclohexanone at a concentration of 10 to 30% by weight. Sulfonium salt or organic sulfonic acid (0.1 to 10% by weight of copolymer resin), as an inorganic acid generator, is added to the copolymer resin solution. The mixture was then filtered with ultra-micro filter to prepare photoresist solution. The inorganic acid generators which can be used in the process include triphenylsulfonium triplate, dibutylnaphthylsulfonium triplate, 2,6-dimethylphenylsulfonate, bis(arylsulfonyl)-diazomethane, oxime sulfonate, 2,1-diazonaphthoquinon-4-sulfonate, or the like. The photoresist solution is spin-coated on a silicon wafer to prepare a thin film, which is then preheated in an oven or on a heating plate at 80-150 EC for 1-5 minutes, exposed to light by using far ultraviolet exposer or an eximer laser exposer, and post-heated at a temperature between 100 EC and 200 EC for 1 second to 5 minutes. The exposed wafer is impregnated in 2.38% aqueous TMAH solution for 1 to 1.5 minutes to obtain a positive photoresist pattern.